Production of paper pulp



'pared a dilute Patented Feb. 19, 1935 UNITED STATES 1,991,824 raonucrioir or rarna rm Francis H. Snyder,

Niagara Falls,

N. Y., assignor to Snyder Maclaren Processes, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application August 11, 1933,

Serial No.

4Claims.

This invention relates to the production of paper pulp and more particularly to a process of bleaching vegetable fibrous material such as wood pulp, lute, straw and the like, and particularly ground wood pulp.

This invention is an improvement on the process covered in my copending application Serial No. 630,477, filed August 25, 1932, now abandoned.

In the copending application referred to above I disclose a process of bleaching fibrous material of the above'referred to character wherein finely divided zinc is contacted with available sulfur dioxide in a liquid suspension of the vegetable fibrous material under treatment. In the preferrcd practice of that process there is first preaqueous suspension of the fibrous material to be treated, such as ground wood pulp, and commercial zinc dust is distributed substantially uniformly throughout the suspension, as by means of agitation, after which there is added to the suspension materialcontaining available SO: radicle, such as sulfurous acid. As a result of this process the product is bleached to a cream white and is brightened in a very short .period of time.

While the foregoing process produces satisfactory results when the bleached pulp is promptly used and when the process is carried out. under carefully controlled conditions, I have found that in commercial practice my former process may be attended with certain disadvantages. In the first place, when the bleached pulp was passed to a chest for supplying fiber in a paper making process, and the pulp remained in storage in such chest for a substantial period of time before passing through the paper making operation, the pulp would become somewhat discolored. Moreover, it was found that if the operator introduced an excessive amount of sulfur dioxide into the beater during the bleaching operation, when the bleached pulp was passed in contact with the metal pipes or metal containers in the paper making operation and when the stock was passed over the machine wire the paper produced would be somewhat brownish in color apparently due to a reaction of the acid in the pulp with the metal in which it had come in contact. The primary object of the present invention is to overcome these disadvantages of my former process while retaining all of the advantages of that process.

In the present process, the bleaching is conducted in substantially the same manner as in the process described in my copending application Serial No. pletion of the 630,477. However, upon the comb leaching operation I add to the beater a liquid suspension of a finely divided insoluble alkali such as an alkaline earth metal carbonate, notably calcium or magnesium carbonate.

The insoluble alkali is intimately mixed with the fibrous material, as by means of agitation, and the excess liquid is separated from the fiber without permitting the mass to stand for suflicient time to allow the insoluble alkali to separate out. The result of this process is that the acid in the suspension is neutralized without raising the pH of the suspension which would be detrimental to the quality of the pulp produced. Moreover, the calcium carbonate, which is preferably employed, or other insoluble alkali, remains mixed with the pulp. This pulp may be delivered to a paper machine apparatus or, if desired, it may be dried into laps or sheets of pulp. In either case, the pulp willcontain the reaction product of the zinc and available sulfur dio' de, l. e. zinc hydrosulfitc, and the calcium carbonate or other insoluble alkali.

As a specific example of my new process, it is preferable to initially prepare a 4 or 5 per cent. suspension of pulp by introducing the fibrous material, such as ground wood pulp, into a conventional paper beater charged with sufiicient water to provide the desired suspension. With the beater wheel running, finely divided zinc, and preferably zinc dust suspended in water, is slowly added to the beater. Depending upon the mateo rial treated, from 5 to 25 pounds of finely divided zinc per ton of dry fiber, and preferably 1-12 pounds of zinc dust per ton of fiber, are added, the zinc dust advantageouslybeing suspended in from 20 to parts of water by weight. In order 35 to secure a substantially uniform distribution of the zinc through the suspension, the heater is permitted to operate for several minutes before further treatment.

When the zinc dust has been satisfactorily dis- 4 tributed, a dilute solution of sulfur dioxide in water is then added. A solution of from 3 to 5 per cent. by weight of sulfur dioxide in water has been found to be satisfactoryand sufficient of such solution is added to introduce from 1 to 2 5 parts by weight of sulfur dioxide to each part by weight of zinc present. In place of the sulfurous acid, any other material containing available 502 radicle may be added to the suspension, such as a bisulfite, e. g. sodium or calcium bisulfite. How- 5 ever, I have found the use of the sulfur dioxide solution described above to be wholly satisfactory and its use is recommended.

The bleaching of the stock is completed almost instantly after the foregoing treatment and, in

any event, it is necessary to continue operating the paper only for several minutes after all of the sulfur dioxide has been added. Thereupon, from 10 to 100 pounds, and preferably about pounds, of very finely divided calcium carbonate is added to the operating beater in substantially the same manner in which a clay suspension is added in a conventional paper making process.

After the calcium carbonate or other insoluble alkali has been added the material may be left in the beater and conventional materials to make up a paper mix added directly thereto. In other wards, the suspension present in the beater may be used as the conventional dilute suspension initially prepared in the paper making operation.

I have found that as a result of the foregoing process, very white newsprint may be prepared from the ground wood pulp or other stock which, in the absence of the foregoing treatment, would produce off-color paper. Moreover, the paper is of high grade and retains its white color over long periods.

While I have described in detail the preferred practice of my process it is to be understood that the details of procedure may be variously modified without departing from the spirit of the in-- vention or the scope of the subjoined claims.

I claim:

1. The process of producing improved paper pulp from fibrous vegetable material which comprises contacting finely divided zinc with available sulfur dioxide in a liquid suspension of said fibrous material, and thereafter distributing throughout the suspension finely divided alkaline earth metal carbonate.

2. The process of producing improved paper pulp from fibrous vegetable material which comprises contacting finely divided zinc with available sulfur dioxide in a liquid suspension of said fibrous material, and thereafter distributing throughout the suspension finely divided calcium carbonate.

3. A process of the character described which comprises initially preparing a dilute aqueous suspension of ground wood pulp, thereafter distributing zinc dust through said on, thereafter adding available sulfur dioxide thereto, and thereafter mixing with the mass a liquid suspension of finely divided alkaline earth metal carbonate.

4. A process of the character described which comprises initially preparing a dilute aqueous suspension of ground wood pulp. thereafter diatributing zinc dust through said thereafter adding available sulfur dioxide thereto, and thereafter mixing with the mass a liquid suspension of finely divided calcium carbonate.

I FRANCIS K. SNYDER, 

